1. Field of the Invention
The present invention relates to a gamma voltage generation circuit. More particularly, the present invention relates to a gamma voltage generation circuit which can adjust voltage levels of output gamma voltages.
2. Description of Related Art
In a present information society, as information communication media and various electronic display devices are widely used in industrial apparatus or home appliances, the electronic display devices become indispensable, and the electronic display devices are continually updated to meet various demands of the information society.
Generally, the electronic display device displays and transmits various information to users. Namely, the electronic device can convert electronic information signals into optical information signals that can be visually recognized by the user.
In a present display device or a system, for example, a cathode-ray tube (CRT) or a liquid crystal display (LCD), a relationship between an input voltage and a display output thereof is not linear, and the relationship between the input voltage and the display output can be described by a gamma curve. Regarding the LCD, an output voltage (i.e. a gamma voltage) corresponding to each of gray levels can be found according to the gamma curve, and by outputting the corresponding gamma voltage, a LCD panel thereof can display a correct gray level, so that the LCD can correctly display images.
To improve a display effect of the LCD, some of the LCD panels can divide a single pixel into two sub pixels. Common voltage levels of the two sub pixels are probably different due to a design of a circuit structure. In this case, when a same gamma voltage is output to the LCD panel, display effects (for example, brightness) of the two sub pixels can be different, so that a display quality thereof is influenced. Therefore, to make different sub pixels to present a same display effect, levels of the output gamma voltages are probably different. Namely, when some of the pixels present the same display effect, displaced gamma voltages have to be received.
FIG. 1 is a circuit schematic diagram illustrating a conventional gamma voltage generation circuit. Referring to FIG. 1, a voltage between a level voltage GMAH and a level voltage BGMAL can be divided by resistors CR0-CR64 to output gamma reference voltages CV0-CV63, wherein the gamma reference voltage CV1 is equal to a level voltage AGMAL, and the level voltage AGMAL is higher than the level voltage BGMAL. Switches 110_1-110_64 select to output the gamma reference voltages CV0-CV63 to serve as gamma voltages V0-V63, or output the gamma reference voltages CV1-CV64 to serve as the gamma voltages V0-V63 according to a control signal S1. A digital-to-analog converter (DAC) 130 selects to output one of the gamma voltages V0-V63 to serve as a driving voltage. However, since resistances of the resistors CR0-CR64 are different, a voltage difference between the gamma reference voltage CV0 and the gamma reference voltage CV1 is different to a voltage difference between the gamma reference voltage CV1 and the gamma reference voltage CV2. Therefore, a display effect of a gray level in case that the gamma reference voltages CV0-CV63 are taken as the gamma voltages V0-V63 is different to a display effect of the same gray level in case that the gamma reference voltages CV1-CV64 are taken as the gamma voltages V0-V63.